I substituted buttermilk for the milk in this recipe, which made for a brilliant muffin. Although, I've also used regular milk with great results.
The muffins last at room temperature for up to 3 days, however, these freeze beautifully. Place on a baking sheet in a single layer and freeze for 1 hour, then transfer to a freezer bag to store up to 1 month. Thaw in the microwave for 10-15 seconds.